The metal working industry utilizes large amounts of oils to assist in the forming of metal parts. Such oils are generally utilized in the form of what is referred to as soluble or emulsifiable oils, employed in the form of oil-in-water emulsions. These emulsions typically contain 80-99% water and are employed as cutting fluids, coolants and lubricants in machining, grinding, drilling, pressing or other metal working applications. The oil used is usually napthenic base, low to medium viscosity and generally includes approximately 10-30% of emulsifiers, rust inhibitors and various other ancillary ingredients. These oils and emulsions are well-known to those of skill in the art and need not be elaborated upon in any greater detail herein.
In most large-scale metal working operations, metal working fluids are collected and recycled, typically in large tanks or pits. Debris is filtered or skimmed therefrom, other impurities removed and the fluids are returned to service. Problems occur owing to various chemical changes in metal working fluids, which changes detrimentally affect the function of the fluids.
The oil-in-water emulsion can provide an ideal growth medium for bacteria, algae or other microbes and such biological contamination is one major source of metal working bath contamination. Biological contamination can result in loss of lubricating power, breaking of the emulsion and separation of the bath into aqueous and oily components. Microbial contamination can also cause the generation of noxious odors and decomposition of the components of the bath. Contamination can result in a cycle of bath degradation; bacteria attack the emulsifiers degrading bath lubricity and breaking the emulsion; furthermore, bacterial growth generates hydrogen sulfide or other sulfur bearing compounds which corrode metal parts, provide a health hazard and serve to reduce the pH of the metal working bath. The reduced pH in turn causes further emulsion breakdown and the sulfides can nourish the growth of algae further degrading bath performance. Such contamination can result in a runaway cycle which can damage expensive equipment and which inevitably necessitates costly disposal of contaminated baths. The addition of strong bases to contaminated baths only temporarily raises the pH. The contaminating organisms quickly generate more acidic sulfide compounds further degrading the bath.
In many instances, sulfur or sulfur containing additives are added to the cutting oils to improve lubricity, machinability and subsequent finish of processed articles. The addition of free sulfur causes the formation of sulfides at a very speedy rate and these types of cutting oils have a historically short life span. Use of the additive of the present invention greatly retards sulfide formation and greatly extends the life of the bath.
Many attempts have heretofore been made to control the growth of organisms in metal working baths. For example, U.S. Pat. No. 3,244,630 discloses the introduction of iodine vapor into a metal working bath for control of micro organisms. Iodine is toxic, hard to handle and corrosive to a variety of metals. Furthermore, iodine can chemically react with and degrade bath components. Consequently, this method has not found widespread acceptance.
U.S. Pat. No. 3,365,397 discloses another prior art approach to microbial contamination of metal working baths which relies upon the use of phenol as a bactericide. Phenol is a toxic compound and furthermore is of limited bactericidal use, since there are a variety of micro organisms which can metabolize phenol.
U.S. Pat. No. 3,240,701 discloses the use of aminoacetic acid compounds such as diethylenatriamine pentaacetic and 1, 2-diaminocyclohexamine tetraacetic acid chelates of metal ions. These compounds are utilized to inhibit the growth of bacteria; however, they have the undesirable property of reacting with zinc which is often present in the metal working baths. This is a significant problem since lubricating oils are frequently enhanced with zinc containing additives such as zinc dialkyldithiophosphate (ZDTP). Such ZDTP additives enhance the lubricity and antiwear properties of the oil. Zinc containing lubricating oils frequently leak into cutting oil baths. Presence of zinc chelating compounds is obviously undesirable in stabilizers or additives, for metal working fluids.
U.S. Pat. No. 4,129,509 discloses the use of complexes of copper ion with polyhydroxy compounds such as citric acid, for purposes of inhibiting microbes. As is set forth in the specification thereof, these complexes exhibit a sigmoidal decomposition over a varying pH range wherein the decomposition of the complex, and subsequent release of metal, increases very sharply over a given portion of the pH range. The complexes of the '509 patent also suffer from the shortcomings of complexing zinc and are therefore limited in utility.
From the foregoing it should be clear that there is a need for a metal working fluid additive which functions to inhibit the growth of undesirable microbes in an oil-in-water bath. It is further desirable that any such compound be of low toxicity, easy to handle, non-corrosive to metals and non-chelating of zinc. In general, the additives of the present invention include complexes formed from the reaction of copper salts with alkanolamines as well as the reaction product of molybdenum salts with alkanolamines. Such compounds exhibit high levels of microbial inhibition and furthermore are non-corrosive, easy to handle and of low toxicity. Most importantly, the copper and molybdenum containing complexes of the present invention do not chelate zinc. This selective chelating ability makes the present invention very useful with all currently employed metal working fluids.
The use of alkanolamine complexes of copper for the control of algae in streams and other bodies of water is shown in U.S. Pat. No. 2,734,028; however, there is no teaching whatsoever in that patent of the use of such compounds in conjunction with metal working fluids, nor is there any teaching or suggestion of the use of molybdenum complexes for any purpose whatsoever.
The present invention fulfills a long-felt need for a low-cost, safe, non-corrosive and simple to use conditioning additive which is compatible with a wide variety of metal working baths, particularly zinc contaminated baths. These and other advantages of the present invention will be presently apparent from the discussion, examples and claims which follow hereinbelow.